Process of dewaxing liquid hydrocarbons



thereof.

Patented May 25, 1937 UNITED STATES PATENT OFFICE PROCESS OF DEWAXING LIQUID HYDRO- CARBONS No Drawing. Application April 26, 1935, Serial No.'18,453. In Sweden May 26, I934 10 Claims.

-the basic principle of which consists in chilling the oil in order to precipitate the wax in solid form. It has long been known. to remove the wax precipitated in solid form by filtration, but during a more recent period centrifugal separators have found a wide use. The necessary difference in specific gravity between the wax and the liquid in which it is suspended has been effected by adding a liquid which changed the specific gravity of the original liquid, or (to express it more accurately) formed with the liquid a solution having a specific gravity different from that of the liquid. For example, it has long been known to add benzine or naphtha. Upon chilling, the solution of this diluting agent with the constituents of the orginal mixture still remaining fluid makes the fluid constituent substantially lighter than the precipitated waxcontaining constituent, thus facilitating centrifugal separation. More recently a great improvement in the process has been effected by the addition of a high specific gravity solvent, thereby forming with the oil a solution substantially heavier than the precipitated wax-containing constituent, which was then centrifugally removed as the lighter component. This heavy diluting agent consisted of a derivate of chlorinehydrocarbon, such as trichlorethylene, carbontetrachloride, dichlorethane, etc., or mixtures Besides thus forming a solution substantially heavier than the wax, the last-mentioned compounds have a favorable influence on the crystallization of the wax.

It is important that the wax be removed as completely as possible from the oil, as it is desirable to get an oil with a low pour point. Generally it is not so very difiicult to effect the crystallization in such a way that this condition is fulfilled. Experience has shown, however, that there are oils which produce a distillate in which a large proportion of the wax is precipitated in a gelatinous state at low temperature. This gelatinous wax contains a large amount of oil, the result of which is that the agglomerates have a specific gravity which differs only slightly from that of the liquid from which they are precipitated. In order to get a sufiiciently low pour point it is therefore necessary to work at a low throughput in the centrifugal treatment.

The present invention relates to a process by means of which this objection to the described process is avoided. According to the invention two additional liquids of different specific gravities are added, one before and the other after the precipitation. The specific gravities of the two additional liquids should each be on different sides of that of the wax. The greater proportion of the liquid added before the precipitation is retained in the agglomerates formed in the precipitation and determines their specific gravity. The liquid of different specific gravity added after the precipitation should not be given time to diffuse into the agglomerates; that is, the second dilution should be effected shortly before the centrifugal treatment so that no appreciable mixing of the liquid inside and outside the agglomerates can take place, In this way the liquid contained in the agglomerates, and thus also the agglomerates, will be of a given specific gravity, that is, a specific gravity that differs from that of the rest of the liquid, which materially facilitates the separation.

If one works on the principle according to which the wax is separated as the heavier component, it is desirable to add, at the crystallization, a liquid of higher specific gravity than the one added after precipitation, for instance, kerosene or some derivate of chlorine-hydrocarbon. If, on the other hand, one desires to separate the wax as the lighter component, it is advantageous to use a light hydrocarbon. In both cases one thereby attains the advantage that the specific gravity of the liquid contained in the Wax crystals 1 or in the gelatinous wax agglomerates substantially differs from that ofthe liquid in which the Wax is suspended. If benzine is used in the first dilution, the enclosed liquid will consist of a mixture of oil and benzine, that is a liquid which is lighter than the wax. The specific gravity of the agglomerates thus becomes lower than that of the wax, and when a heavy diluent is then added the difference in specific gravity becomes considerable. The conditions will of course be the same if one uses for instance trichlorethylene in the first dilution and benzine in the second dilution, the only difference then being that the Wax agglomerates have a higher specific gravity than the liquid.

On the condition that the addition of liquid after the precipitation is made a suficiently short time before the centrifugal treatment so that the liquid contained in the agglomerates cannot be appreciably dilutedby diffusion, it is in some cases possible to dispense with the dilution before the precipitation, as the difference in specific gravity is sufiiciently great also without taking this measure.

The procedure is particularly advantageous in the removal of wax which precipitates in gelatinous form; but, also, in case more compact wax-masses are obtained in the precipitation, the procedure offers great advantages, as also these masses contain some amount of mother solution. By working according to the present procedure, it becomes possible to treat products from which the wax could not previously be removed to advantage by centrifugal treatment, because a large proportion of the wax was precipitated in gelatinous form. When using the procedure in connection with oils in which the wax is precipitated in more compact form, it is possible either to economize the dilution agent or to let the centrifuges work at a high throughput.

As mentioned hereinbefore, it is possible to allow the crystallization to take place either directly from the oil without adding any diluent,

or after a diluent has been added. The first method is mainly used in the treatment of oils of low viscosity and comparatively low wax content. In treating oils of high viscosity, or oils of low viscosity but high content of wax, it is generally necessary to add a diluent in order to obtain a suiiiciently good crystallization. It is a well-known fact that the size of the crystals is strongly influenced by the viscosity of the liquids from which they are precipitated.

As stated, the second diluent is added after the temperature of the oil has been lowered below the point at which the gelatinous wax is precipitated. It is of course suitable to chill the diluent, before its addition, to a temperature which is the same as that of the oil.

It will be understood that the invention is not limited to the use of additional liquids of different specific gravities. The characteristic feature is that the specific gravity of the liquid mixture of hydrocarbons is changed in one direction before the precipitation and in the opposite direction after the precipitation. The means by which this change is effected are of secondary impor-- tance.

A specific example is given below:

100 parts by volume of wax-containing lubricating oil with a spec. gravity of .92 were mixed with 20 parts by volume of benzine with a spec. gravity of .75. The solution obtained in this way had a spec. gravity of .89. It was chilled, under stirring, down to 25 C. causing a precipitation of the wax. The solution was rapidly mixed with 140 parts by volume of trichlorethylene and at once separated in a centrifugal. The wax separated out was found to contain considerable quantities of benzine.

At a comparative trial with the same oil carried out by dissolving 100 parts by volume of oil in 140 parts by volume of trichlorethylene and chilling in the same Way, and separating in the same centrifugal, it was necessary to reduce the capacity by about 15% in order to obtain the same separating effect.

The explanation must be that benzine adheres to the wax crystals forming with them bodies, the spec. gravity of which is considerably lower than that of the wax.

What I claim and desire to protect by Letters Patent is:

1. Method of removing from liquid mixtures of hydrocarbons, hydrocarbons which precipitate in solid form on cooling, characterized in that the liquid is diluted before precipitation, with a normally liquid agent which changes the specific gravity of the liquid in one direction, and after the precipitation with another normally liquid agent which changes the specific gravity of the liquid in the opposite direction, whereupon the precipitated hydrocarbons are removed by centrifugation.

2. Method according to claim 1, characterized in that the diluent used before the precipitation consists of an agent which is lighter than the precipitated hydrocarbons, and that the diluent used after the precipitation consists of an agent which is heavier than the precipitated hydrocarbons.

3. Method according to claim 1, characterized in that the diluent used before the precipitation consists of an agent which is heavier than the precipitated hydrocarbons, and that the diluent used after the precipitation consists of an agent which is lighter than the precipitated hydrocarbons.

4. Method according to claim 1, characterized in that the dilution after the precipitation is made such a short time before the centrifugal treatment that the liquid contained in the agglomerates of precipitated hydrocarbons cannot be appreciably diluted by diffusion by the last addition of diluent.

5. In the process of treating wax-bearing oil to separate wax therefrom wherein the oil is chilled to precipitate the wax constituent and wherein is added, usually before chilling, a normally liquid diluting agent which affects the relative specific gravities of the two constituents and wherein the constituents are then centrifugally separated; the improvement which consists in adding normally liquid diluting agents of the character specified at two different stages of the process, namely, before chilling and precipitation and after precipitation and before centrifugation to effect a predetermined change in the specific gravity of the constituent not precipitated to effect a substantial increase in the difference between the specific gravities of the two constituents before and during centrifugation.

6. The process in accordance with claim 5 wherein the diluting agent that is added before chilling is of substantially higher specific gravity than that of the wax-containing constituent and wherein the diluting agent added after precipitation is of substantially lower specific gravity than that of the precipitated wax constituent.

7. The process in accordance with claim 5 wherein the diluting agent that is added before chilling is of substantially lower specific gravity than that of the wax-containing constituent and wherein the diluting agent added after precipitation is of substantially higher specific gravity than that of the precipitated wax constituent.

8. The process in accordance with claim 5 wherein the addition of the diluting agent after precipitation is made so short a time before the centrifugal treatment that the fluid hydrocarbons contained in the agglomerates of precipitated hydrocarbons cannot be substantially diluted by diffusion by said addition.

9. In the process of treating wax-bearing oil to separate wax therefrom wherein the oil is chilled to precipitate the wax constituent and wherein is added, usually before chilling, a diluting agent which afiects the relative specific gravities of the two constituents and wherein the constituents are then centrifugally separated; the improvement, particularly applicable to mixtures in which the wax constituent is precipitated as a gelatinous agglomerate, which comprises adding two diluting agents, both normally liquid, of specific gravities respectively substantially higher and substantially lower than the specific gravity of the wax, one of which diluting agents is added to the oil before chilling and precipitation and the other of which is added after chilling and precipitation and within so short a time prior to centrifugation that it dissolves mainly in the constituent not precipitated, whereby a pronounced difference in the specific gravities of the two constituents is maintained during centrifugation.

10. In the process of treating wax-bearing oil to separate wax therefrom wherein the oil is chilled to precipitate the wax constituents and wherein is added, before or after chilling but before centrifugation, a normally liquid diluting agent which afi'ects the relative specific gravities of the two constituents and wherein the constituents are then centrifugally separated; the improvement which consists in adding two different normally liquid diluting agents of the character specified, one of which agents is of substantially lower specific gravity, and the other of which is of substantially higher specific gravity, than constituents of the oil, and in adding said agents at difierent stages of the process, one of said agents changing the specific gravity of the liquid in one direction and the other of which is added after precipitation and changes the specific gravity of the liquid in the other direction.

HANS OLOF LINDGREN. 

